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Zero-Knowledge Proofs

Prove Without Revealing

13 min read Updated 2024

What Are ZK Proofs?

Zero-knowledge proofs let you prove you know something (a secret, a solution) without revealing what that something is. The verifier learns nothing except that the statement is true.

Classic Example: Ali Baba's Cave
Cave with two paths meeting at a magic door
Peggy (prover) knows the secret word
Victor (verifier) waits at entrance

1. Peggy enters, takes random path (A or B)
2. Victor calls out which path to return from
3. If Peggy knows secret, she always succeeds
4. Repeat many times → probability of luck → 0

Properties

Completeness

True statements can always be proven

Validity

Soundness

False statements cannot be proven

Security

Zero-Knowledge

Verifier learns nothing else

Privacy

Types of ZK Proofs

InteractiveMultiple rounds of communication required
Non-Interactive (NIZK)Single message proof
zk-SNARKsSuccinct, fast verification (used in Zcash)
zk-STARKsNo trusted setup, quantum resistant
BulletproofsShort proofs, no trusted setup

Applications

  • Private cryptocurrencies (Zcash, Monero)
  • Authentication without passwords
  • Age verification without revealing age
  • Private voting systems
  • Blockchain scaling (ZK-rollups)
  • Anonymous credentials